Electrotherapeutic Modalities: TENS, Ultrasound, and Stimulation in Physiotherapy

You’ve probably seen these electrodes attached to a patient’s skin or heard about TENS and ultrasound in physical therapy. These electrotherapy modalities raise a lot of questions: Are they really effective? How do they work? For which conditions?

At Physioactif, we use a variety of therapeutic modalities as part of a comprehensive, evidence-based approach. Electrotherapy modalities such as TENS and ultrasound can play a complementary role in certain situations, always in combination with active treatment approaches.

In this article, you’ll learn what electrotherapy modalities are, how they work physiologically, which conditions can benefit from these treatments, and what scientific research says about their actual effectiveness.

What are electrotherapy modalities?

Electrotherapy modalities include techniques that use electrical energy or high-frequency sound waves to treat pain and inflammation. The main ones are TENS (transcutaneous electrical nerve stimulation), therapeutic ultrasound, and interferential currents.

Electrotherapy is one of the passive modalities used in physical therapy. Unlike therapeutic exercises, in which you are actively involved, these techniques apply an external form of energy to your body to produce therapeutic effects. They are used to complement active approaches, never as a standalone treatment.

The three main methods

TENS (Transcutaneous Electrical Nerve Stimulation) uses a low-frequency electrical current (0 to 200 Hz) applied to the skin via adhesive electrodes. Its primary purpose is pain management by modulating the transmission of nerve signals. You will feel a tingling sensation or slight vibrations during the treatment.

Therapeutic ultrasound uses high-frequency sound waves (1 to 3 MHz), well beyond the range of human hearing. These waves penetrate deep into the tissues and create mechanical and thermal effects that reduce inflammation, promote tissue healing, and improve circulation.

Interferential currents combine two medium-frequency currents (4000 Hz) that cross paths within the tissue, creating a modulation that penetrates deeply. This modality is used for pain management, muscle recovery, and edema reduction.

Role in the treatment plan

These modalities are considered adjunctive, meaning they complement other interventions rather than serving as the primary treatment. According to current physical therapy guidelines, therapeutic exercises and active approaches remain central to the treatment plan for most musculoskeletal conditions.

Electrotherapy is most commonly used in two situations: during the acute phase of an injury, when severe pain limits your ability to move and exercise, and for short-term symptom management as you progress through your active rehabilitation program.

How do electrotherapy modalities work?

TENS blocks the transmission of pain signals at the spinal cord (gate control theory) and stimulates the production of endorphins. Ultrasound creates micro-movements in the tissue that improve circulation and reduce inflammation.

TENS: Mechanisms of Action

Transcutaneous electrical nerve stimulation works through two well-documented primary mechanisms.

Gate Control Theory explains the most immediate mechanism of TENS. When you apply an electrical current, it stimulates the large A-beta nerve fibers that transmit tactile sensations. These fibers conduct signals more quickly than the fibers that transmit pain.

At the level of the spinal cord, these rapid signals close the gate and block the transmission of pain signals to the brain. It’s a bit like when you bump your elbow and instinctively rub it: the sensation of rubbing alleviates the pain. The effect is usually immediate but temporary.

The endorphin mechanism works differently. By applying a low-frequency current (less than 10 Hz) at a higher intensity that causes a slight muscle contraction, you stimulate the release of endorphins and enkephalins, your body’s natural opioids.

This mechanism takes longer to take effect (20 to 40 minutes), but provides relief that can last for several hours after the device is turned off.

Ultrasound: Physiological Mechanisms

Therapeutic ultrasound works differently depending on whether it is used in continuous or pulsed mode.

The mechanical (non-thermal) effect occurs when high-frequency sound waves pass through your tissues. These waves create micro-movements and vibrations at the cellular level that increase the permeability of cell membranes, promoting metabolic exchange. Your cells are better able to absorb nutrients and eliminate waste.

The thermal effect (continuous mode) occurs when molecular vibrations generated by ultrasound produce heat in deep tissues. This heat reaches structures such as tendons, ligaments, and joint capsules, improving blood circulation, relaxing connective tissues, and reducing muscle spasms.

The biological effects include stimulating tissue repair (particularly in tendons and ligaments), reducing chronic inflammation, improving lymphatic drainage, and softening scar tissue.

What conditions are treated with electrotherapy?

Electrotherapy is used to treat lower back pain, neck pain, osteoarthritis, tendonitis, sprains, and acute musculoskeletal injuries. TENS primarily targets pain, while ultrasound targets inflammation and deep tissues.

Indications for TENS

For back and neck pain, TENS is frequently used to treat acute and chronic lower back pain, particularly for lumbar strains and episodes of severe pain. It also helps with neck and upper back pain.

In cases of osteoarthritis (knee, hip, lower back), TENS can help manage pain. Although it does not treat the joint degeneration itself, it can make daily activities and strengthening exercises more bearable.

For acute injuries and specific conditions, it is used to treat sprains, various types of tendonitis, carpal tunnel syndrome, and post-operative pain.

Indications for ultrasound

Tendinitis is a common indication, particularly in the shoulder, elbow (epicondylitis), knee, and Achilles tendon. Calcific tendinitis of the shoulder responds particularly well to ultrasound, with studies showing short-term benefits in dissolving calcium deposits.

Chronic bursitis, adhesive capsulitis (frozen shoulder), deep tissue inflammation, localized edema, and persistent muscle spasms can all benefit from ultrasound therapy.

In tissue healing, ultrasound promotes the repair of injured tendons and ligaments, helps soften scar tissue, and can reduce post-surgical adhesions.

Important Contraindications

For TENS: Never use if you have a pacemaker, during pregnancy (on the abdomen), if you have epilepsy, or on an area affected by venous thrombosis.

For ultrasound: Never during pregnancy (fetal area), on active cancer or tumors, areas of bone growth (children), deep vein thrombosis, the heart, the eyes, reproductive organs, or active infections.

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What happens during an electrotherapy session?

An electrotherapy session begins with an assessment of your condition. The physical therapist places the electrodes (TENS) or applies the conductive gel (ultrasound), adjusts the settings, and monitors how you feel for 10 to 20 minutes.

A typical TENS session

The initial assessment (5 to 10 minutes) allows us to discuss your symptoms, pinpoint the exact location of the pain, check for any contraindications, and select the appropriate settings (frequency and intensity).

Preparation (2–3 minutes) involves cleansing the skin to remove any oil. The therapist then places 2 to 4 electrodes around or on the painful area.

During treatment (10–30 minutes), the device starts at a low intensity and gradually increases until you feel a comfortable tingling sensation. Constant communication with your therapist ensures that the sensation remains comfortable.

A typical ultrasound exam

The assessment (5 minutes) determines the exact area, the depth of the target tissues, and the appropriate mode (pulsed or continuous).

Preparation (1–2 minutes) includes applying a conductive gel, which is essential for wave transmission.

The treatment (5–15 minutes) involves a continuous circular motion of the device head. In continuous mode, you will feel a gentle warmth. In pulsed mode, you generally won’t feel anything.

Treatment Frequency and Duration

The standard protocol recommends 2 to 3 sessions per week for a total duration of 2 to 6 weeks, with a reassessment after 4 to 6 sessions.

TENS can be used at home with a personal device, but training from your physical therapist is strongly recommended.

FAQ on Electrotherapy Modalities

Is electrotherapy really effective?

Effectiveness varies depending on the condition and the individual. Research paints a nuanced picture.

For TENS, studies show a moderate effect on acute pain in the short term. Its effectiveness is limited when used as a standalone treatment. The best results are achieved when combined with active interventions. Some studies have found that the effect was not significantly greater than that of a placebo.

When it comes to ultrasound, the evidence is even more mixed. A Cochrane review found a possible benefit for calcific tendinitis in the short term, but the evidence remains of limited quality. In 2021, NICE (National Institute for Health and Care Excellence) recommended against offering ultrasound for primary chronic pain.

Current guidelines recommend using these approaches as adjuncts, never as the primary treatment. Therapeutic exercises remain the priority.

How long does a session last?

TENS: 10 to 30 minutes
Ultrasound: 5 to 15 minutes per area
Interferential currents: 15 to 20 minutes

A full physical therapy session, including assessment and other treatments, typically lasts 30 to 60 minutes.

Does it hurt?

No, electrotherapy should never be painful.

With TENS, you will feel a tingling, vibrating, or prickling sensation. The intensity is adjusted to your comfort level. With ultrasound, the continuous mode creates a gentle, pleasant warmth. The pulsed mode generally produces no sensation.

If you experience pain, significant discomfort, or a burning sensation, notify your therapist immediately.

Can you use a TENS machine at home?

Yes, these devices are available over the counter at pharmacies. However, training from a physical therapist is strongly recommended to learn the correct placement of the electrodes, understand the contraindications, and adjust the settings safely.

Home use is suitable for occasional symptom management between sessions. Home TENS therapy is not a substitute for your exercise program or professional care.

Is electrotherapy covered by insurance?

Private insurance plans generally cover electrotherapy as part of physical therapy sessions. The cost is included in the session fee, with no separate additional charges.

The SAAQ and the CNESST cover electrotherapy if it is recommended by your physical therapist.

Public health insurance (RAMQ) does not directly cover physical therapy at private clinics, including electrotherapy.

Are there any side effects?

Side effects are rare and generally mild.

With TENS: mild skin irritation, temporary redness, allergic reaction to the gel (rare).

With ultrasound: temporary redness, discomfort if the intensity is too high. No long-term side effects have been reported.

Always tell your therapist about any unusual reactions.

How many sessions are needed?

The number of sessions varies depending on the type of condition (acute: 4 to 8 sessions; chronic: 8 to 12 sessions), the severity of your symptoms, and your individual response.

A reassessment after 4 to 6 sessions allows us to adjust the treatment plan. Electrotherapy is used as a complementary treatment. Your exercise program remains the central component.

What is the difference between TENS and interferential currents?

TENS uses a low frequency (0–200 Hz) that targets the skin's surface and nerves. It is portable and can be used at home.

Interferential currents use a higher fundamental frequency (4000 Hz) and penetrate deeper into the tissue. They are better tolerated at high intensities but are currently used only in clinical settings.

Both aim to manage pain through slightly different mechanisms.

Our physical therapists can assess your condition and provide you with a personalized treatment plan.

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Conclusion

Electrotherapeutic modalities such as TENS and ultrasound can play a useful role in pain management and certain musculoskeletal conditions, especially when used in conjunction with an active exercise program. Although the scientific evidence regarding their effectiveness when used alone is mixed, they remain valuable tools for short-term symptomatic relief.

If you are experiencing persistent pain or a musculoskeletal injury, consult a physical therapist to determine whether these treatments could be incorporated into your overall treatment plan. The most effective approach remains a combination of passive treatments and active interventions tailored to your specific condition.

Understanding the anatomy of the spine can help you better grasp how these treatments affect your tissues. For specific conditions such as a herniated disc or other back problems, a comprehensive evaluation will help determine the best course of action for your recovery.